The number of particles in a fluid sample, their size, and shape (morphology) can be determined by an imaging apparatus as shown, for example, in U.S. Pat. Nos. 5,572,320; 7,385,694; 5,627,905; 5,959,668; 6,049,381; 6,104,483; 6,501,504; 6,873,411; 7,019,834; 7,184,141; 7,307,717; 7,385,694; 7,921,739; 8,056,400 and 8,079,250 all incorporated herein by this reference. There is typically, however, no differentiation made between magnetic and non-magnetic particles. This information is important to maintenance personnel.
Magnetometers can be used to determine the overall percent of ferromagnetic particles in oil, or to provide information regarding the size and magnetic nature (ferromagnetic or non-ferromagnetic) of individual particles greater than a certain minimum size threshold. See, for example, U.S. Pat. Nos. 5,001,424; 5,315,243; 5,444,367; 5,404,100; 5,811,664 and 6,051,970 all incorporated herein by this reference. Such devices, however, do not classify the magnetic particles according to morphology. In addition, such devices typically either supply an overall ferromagnetic percent or information regarding individually observed particulate, but not both.